1. Field of the Invention
The present invention relates generally to a small twin spool gas turbine engine, and more specifically to fan blade to rotor shaft connection of a gas turbine engine.
2. Description of the Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98
In a twin spool gas turbine engine, a low speed rotor shaft connects a low pressure turbine to the low pressure compressor which is typically a fan blade assembly. A high speed rotor shaft connects the high pressure turbine to the high pressure compressor. The high speed rotor shaft rotates around the inner low speed rotor shaft. Both rotor shafts are supported by bearings on the ends of the shafts.
In a small gas turbine engine, such as the size used to power an unmanned aero vehicle (UAV), the engine is so small that the rotor shafts will rotate at very high speeds. Also, to reduce the size of the engine the spacing between the forward and aft bearings is reduced to control the rotor dynamics problems that arise due to the high rotation speeds. The bearings that support the rotor shafts are thus exposed to very high temperatures and require cooling in order to make such a small engine possible.
At these high rotation speeds, the rotor shafts are also subject to high levels of vibration that must be addressed in the design to also make the small engine possible.